Third Nerve Palsy Flashcards
Neurogenic
What type of deviation do you expect in a third nerve palsy?
Exotropia + Hypotropia in complete 3rd + ptosis (ptosis, and maybe dilation of pupil and accommodation palsy)
Superior division 3rd = hypotropia + ptosis (LP)
Inferior Division 3rd = depends what muscles are affected ;
- Isolated IR palsy = hypertropia
- Isolated MR palsy = Exotropia
- Isolated IO = hypotropia with possible slight eso.
Ciliary ganglion - pupil dilated
Pathway of third nerve
- Begins in the oculomotor nucleus is a cluster of individual muscle subnuclei and Edinger-Westphal nuclei in the dorsal midbrain
- The neuron axons traverse anteriorly within the third nerve fascicle and exit midbrain near medial aspect of the cerebral peduncle.
- It enters the subarachnoid space, where it travels between the superior cerebellar artery and the posterior cerebral artery, and
travels medially along the posterior communicating artery and lateral to the internal carotid artery (susceptible to aneurism). - Runs anterior through the cavernous sinus where enclosed within lateral wall, above 4th nerve.
- Enters orbit through the superior orbital fissure then divides into 2 (inferior and superior division) at annulus of zinn.
Aetiology of 3rd nerve palsy
- Microvascular
- Trauma
- Secondary to space occupying lesion / tumour
- Aneurysm (if pupil blown, indicates aneurysm, might result in subarachnoid haemorrhage)
- Myasthenia Gravis
- Congenital 3rd
- Inflammatory/viral infection
- Ophthalmic Migraine
What blood tests should be carried out in a px over 50 y/o and the pupil IS involved ?
- BP
- Blood Glucose
- ESR - erythrocyte sedimentation rate (Sign of inflammation/infection)
- MRI with MRA (MR angiography)(angiography = check vessels through circle of Willis + all vessels)
What blood tests should be carried out in a patient over 50 y/o WITHOUT pupil involvement?
- BP
- Blood Glucose
- ESR - erythrocyte sedimentation rate (Sign of inflammation/infection = MS, Rheumatoid Arthritis)
- They should be reviewed closely and if the pupil becomes involved Immediate Scan looking for compressive lesion
How long does it take for a microvascular 3rd to resolve?
- Approx 3-4 months
- If not starting to resolve then MRI/MRA
- Ptosis first to recover = will get diplopia
What do you get with a traumatic or compressive 3rd nerve palsy ?
Pupil involvement
Abberent regeneration (because nerves are damaged and when they regrow, they attach to new muscles)
What are the signs of aberrant regeneration?
Elevation of upper eyelid on down-gaze or attempted adduction (pseudo-von Graefe phenomenon).
Adduction of the eye on attempted up-gaze and sometimes on attempted down-gaze.
Retraction of the globe on up-gaze or down-gaze.
Constriction of the pupil on attempted adduction.
“Pseudo-Argyll Robertson pupil”: greater constriction of pupil to convergence than to light and gaze-evoked pupillary constriction
Why does the pupil become involved in a third nerve palsy?
pupillary fibres run on the outside of the nerve therefore when PCA aneurysm (abnormal swelling or bulge in the wall of an artery) will compress on the third nerve
NEED SCAN ASAP if pupil involved, could have a subarachnoid haemorrhage
what are the signs of an aneurysm?
- Severe headache with sudden onset, will wake up with very sore head (might feel nauseous/being sick)
Loss of consciousness
Pain in or around the eye
if just one nerve affected where is the lesion likely?
At the nucleus
Bilateral Ptosis and Superior Rectus Paresis:
Where is the lesion in 3rd?
Nuclear lesions e.g. R 3rd nucleus palsy causes bilateral ptosis (drooping eyelids) and bilateral paresis (weakness) of the superior rectus muscles, and ipsilateral RMR, RIO, RIR + R pupil!)
The levator is supplied by a common single caudal nucleus; the superior rectus is supplied by the contralateral nucleus; and the medial rectus, inferior rectus and inferior oblique muscles are supplied from the ipsilateral nucleus.
In this setting the bilateral superior rectus weakness can only be confirmed to be of nuclear origin by demonstrating a deficient vestibular input by means of the doll’s head manoeuvre, where neither eye will elevate.
what are fasicular syndromes associated with 3rd np?
Weber’s syndrome: Combination of ipsilateral third nerve palsy and contralateral hemiparesis (weakness to the opposite side of the body) due to damage to the cerebral peduncle and the third nerve (also port-wine stain (red mark on face) and glaucoma).
Benedikt’s syndrome: Combination of ipsilateral third nerve palsy, contralateral hemiparesis, and contralateral ataxia with intention tremor (occurs during voluntary movement towards a target) due to damage to the cerebral peduncle, third nerve, and red nucleus (coordination of movements and the integration of sensory and motor information to facilitate smooth and precise motor control).
how to test if other nerves affected (4th, 5th and 6th)
4th: Confirming the integrity of the fourth nerve can be difficult. The main action of the superior oblique is depression when the eye is adducted. This function cannot be tested properly when adduction is limited. Instead, the patient should be instructed to abduct the eye and then try to look down, when intorsion should be seen if the fourth nerve is intact. Observation of an iris landmark or a conjunctival vessel can aid detection of intorsion.
6th : Even when the eye is very exotropic, it is possible to demonstrate lateral rectus function by observing the saccadic velocity or performing a force generation test.
5th: Reduced corneal sensitivity in association with a third nerve palsy suggests a lesion in the orbit or cavernous sinus
management non surgical in 3rd np
Spontaneous recovery is high in microvascular 3rd nerve palsies. Traumatic 3rds show some improvement but is rarely complete and frequently complicated by aberrant regeneration.
Nonsurgical Treatment:
Prisms are of limited use in complete palsy due to reversibility of diplopia in different positions of gaze or too large deviation, and torsional image. Partial palsy = better chance of BSV with prism.
Occlusion may be used to manage diplopia.
Some px find can easily ignore second image, or some with long-standing can supress.
Tint glasses can help with photophobia from dilated pupil; pilocarpine drops may constrict pupil if necessary. Can also paint CL with small pupil.
Ptosis crutches fitted to spectacles can support ptosis (watch for dry eye)
Botulinum toxin may be used to improve alignment and in investigating BSV potential. It is occasionally effective in restoring long-term alignment of the visual axes when injected into the LR or a vertical rectus in a partial palsy.; repeated injections may be necessary for long-term alignment in partial 3rd. Unlikely to bring about a significant change in alignment in a total palsy.
